Good Idea thobut
Just needs a bit of take up
To be brutally honest, in the vast majority of decent sized/populated conurbations this would never work.
I work in the public transport industry over several modes, mainly bus & my reasoning is this.
Cost.
I can't think of an operator that would likely fund the cost of adapting buses to take a front rack *rear racks are out as that is where the engine bay access panels are situated.
Any adaptations would likely require approvals *vehicle type* DVLA, testing etc incurring further cost.
Any adaptations would incur further insurance risk & therefore cost
*if an insurer would accept such adaptations*
Legal.
Liability for claims against operators for damaged bikes.
Crime.
Any bus carrying bikes would be targeted by scummers.
Logistics/Time.
Loading & unloading takes time.
Many routes operate within very tight time frames with little to zero turnaround time.
There might well be another dozen reasons/examples of how unfeasible this might be.
In low population, mainly rural areas this might have more of a chance of working & on distance coaches also, but I wouldn't hold my breath.